It is well known that amides of organic carboxylic acids of the general formula RCONH.sub.2 can be prepared from the corresponding acids, esters or acid chlorides by suitable reaction with ammonia. In many instances, the preferred method is to convert the nitrile to the amide by hydrolysis which proceeds in the presence of either acid or base. In most instances, however, it is difficult to isolate the amide because the hydrolysis continues further to form the corresponding acid. This is a result of the fact that the rate of hydrolysis of the amide is faster than that of the nitrile. An alternative procedure is to employ a strong acid, such as cold concentrated sulfuric acid, with the nitrile. This procedure has the disadvantage of requiring a molar excess of acid, and base equivalent to the acid, in order to liberate the amide. Another proposal has been to use an alkaline peroxide but at least an equivalent of peroxide is needed and its high cost makes this method unattractive for commercial usage.
More recently, catalytic processes have been developed for the preparation of amides from nitriles. For example, Goetz et al. U.S. Pat. No. 3,670,021 teaches the conversion of organic nitriles to amides by carrying out the hydrolysis reaction in the presence of a noble metal compound such as rhodium chloride which may be employed in the form of a complex thereof with, for example, pyridine, triphenylphosphine, 2,2'-bipyridyl, o-phenanthroline, and the like. A similar process is disclosed in Rauch et al. U.S. Pat. No. 3,673,250 in which a transition metal compound such as rhodium chloride is complexed with an organic phosphine, phosphite such as trialkyl or triarylphosphite, arsine, arsenite, stibine, or antimonite. While these catalysts, and particularly the Rauch et al. catalysts, exhibit a high initial productivity, a rapid deactivation of the catalyst has been observed.
We have now found a new catalyst system which is useful for the conversion of nitriles into amides with excellent conversions and selectivities and which exhibits a dramatically decreased rate of deactivation.
It is the object of this invention to provide a new catalyst for the catalytic hydrolysis of nitriles to amides with high conversions and selectivities for extended periods of time. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.